''Amphibalanus eburneus'', the ivory barnacle or American acorn barnacle, is a

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

of acorn

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive ...

in the family

Balanidae The Balanidae comprise a family of barnacles of the order Balanomorpha. As a result of research published in 2021 by Chan et al., the members of the family Archaeobalanidae were merged with this family. Genera These genera belong to the family B ...

. It occurs on the east coast of North America, the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

and

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United S ...

Description

The ivory barnacle is a medium-sized, cone-shaped

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

barnacle with a white test composed of fused plates. It has a diamond-shaped operculum protected by a hinged lid formed from two triangular halves each consisting of two plates, a tergum and a scutum. It can grow to a height of but most individuals are much smaller. This barnacle can be confused with the white bay barnacle (''

Balanus improvisus ''Amphibalanus improvisus'', the bay barnacle, European acorn barnacle, is a species of acorn barnacle in the family Balanidae. Description ''Amphibalanus improvisus'' has a smooth white or pale grey conical calcareous shell composed of six fuse ...

'') but that species is smaller, only growing to a height of . Another similar species is the striped barnacle (''

Balanus amphitrite ''Amphibalanus amphitrite'' is a species of acorn barnacle in the Balanidae family. Its common names include the striped barnacle, the purple acorn barnacle and Amphitrite's rock barnacle. It is found in warm and temperate waters worldwide. Desc ...

'') but that has vertical pink lines on the test.

Distribution and habitat

The native range of the ivory barnacle extends from

Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native En ...

to the

and

but it has extended this range as a result of

fouling Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms ( biofouling) or a non-living substance (inorganic or organic). Fouling is usually distinguished from other sur ...

the bottoms of ships and because its larvae are sometimes transported in

ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship, ...

water. It was first seen in

Pearl Harbor Pearl Harbor is an American lagoon harbor on the island of Oahu, Hawaii, west of Honolulu. It was often visited by the Naval fleet of the United States, before it was acquired from the Hawaiian Kingdom by the U.S. with the signing of the ...

, Hawaii in 1929 and is now common in all the main islands. It is found, sometimes in great numbers, from low tide mark to depths of attached to hard surfaces including rocks, mollusc shells,

pilings A deep foundation is a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does to a subsurface layer or a range of depths. A pile or piling is a vertical structural eleme ...

jetties A jetty is a structure that projects from land out into water. A jetty may serve as a breakwater, as a walkway, or both; or, in pairs, as a means of constricting a channel. The term derives from the French word ', "thrown", signifying somet ...

and other man-made structures, ships' hulls and the roots of the red mangrove (''

Rhizophora mangle ''Rhizophora mangle'', the red mangrove, is distributed in estuarine ecosystems throughout the tropics. Its viviparous "seeds", in actuality called propagules, become fully mature plants before dropping off the parent tree. These are dispersed b ...

'').

Reproduction

Ivory barnacles tend to aggregate with others and form dense populations. Each one is a

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have ...

but cross fertilisation takes place when an individual protrudes its long penis and inserts it into the operculum of an adjoining individual where eggs have already developed. Sperm is deposited there, and the fertilised eggs are brooded in the mantle cavity. On hatching, the larvae are expelled into the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

and become

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cr ...

ic. They pass through six naupliar stages and one cyprid stage over the course of one to two weeks. The nauplii feed on

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. P ...

but the cyprid larvae do not feed. They search out sites for settlement, possibly following chemical cues from already established adults or testing the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

for suitability. Once settled, they cement themselves by their heads to the surface and undergo metamorphosis into juvenile barnacles.

References

External links

* {{Taxonbar, from=Q2880553, from2=Q13366379 Barnacles Crustaceans of the Atlantic Ocean Crustaceans described in 1841 Taxa named by Augustus Addison Gould